Ionization gauge with operational parameters and geometry designed for high pressure operation

ABSTRACT

An ionization gauge to measure pressure and to reduce sputtering yields includes at least one electron source that generates electrons. The ionization gauge also includes a collector electrode that collects ions formed by the collisions between the electrons and gas molecules. The ionization gauge also includes an anode. An anode bias voltage relative to a bias voltage of a collector electrode is configured to switch at a predetermined pressure to decrease a yield of sputtering collisions.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/860,050, filed Aug. 20, 2010, which is a continuation ofInternational Application No. PCT/US2009/034460, which designated theUnited States and was filed on Feb. 19, 2009, published in English,which application claims the benefit of U.S. Provisional Application No.61/066,631, filed on Feb. 21, 2008.

The entire teachings of the above applications are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

Ionization gauges, more specifically Bayard-Alpert (BA) ionizationgauges, are the most common non-magnetic means of measuring very lowpressures. The gauges have been widely used worldwide. These gauges weredisclosed in 1952 in U.S. Pat. No. 2,605,431, which is hereinincorporated by reference in its entirety. A typical ionization gaugeincludes an electron source, an anode, and an ion collector electrode.For the BA ionization gauge, the electron source is located outside ofan ionization space or anode volume which is defined by a cylindricalanode screen. The ion collector electrode is disposed within the anodevolume. Electrons travel from the electron source to and through theanode, cycle back and forth through the anode, and are consequentlyretained within, or nearby to, the anode.

In their travel, the electrons collide with molecules and atoms of gasthat constitute the atmosphere whose pressure is desired to be measured.This contact between the electrons and the gas creates ions. The ionsare attracted to the ion collector electrode, which is typicallyconnected to ground. The pressure of the gas within the atmosphere canbe calculated from ion and electron currents by the formula P=(1/S)(I_(ion)/I_(electron)), where S is a coefficient with the units of1/Torr and is characteristic of a particular gauge geometry, electricalparameters, and pressure range.

SUMMARY OF THE INVENTION

The operational lifetime of a typical ionization gauge is approximatelyten years when the gauge is operated in benign environments. However,these same gauges and electron sources (cathodes) fail in minutes orhours when operated at too high a pressure or during operation in gastypes that degrade the emission characteristics of the electron source.Cathode interactions with the gauge environment can lead to decreasedoperational life. The oxide coating on the cathode can degrade whenexposed to water vapor. Degradation of the oxide coating dramaticallyreduces the number of electrons generated by the cathode. Exposure towater vapor results in the complete burnout of a tungsten cathode.

Sputtering is also a problem, when operating the ionization gauge athigh pressures, such as above 10⁻⁴ Torr. This is a problem at highpressure since there is more gas to ionize. This sputtering is caused byhigh impact energies between ions and components of the ionization gaugeas has been demonstrated by the inventor. Ions with a high energy mayimpact a tungsten material that forms a collector post of the ionizationgauge. This results in atoms being ejected from the collector post andenvelope surfaces. This ejection carries a significant internal kineticenergy. Ejected material can travel freely to other surfaces within theline of sight of the material, and can cause gauge failure by coatingthe cathode or by coating of the feed-through insulators of the gauge,which can result in electric leakages.

The kinetic energy of the ions generated in a Bayard-Alpert ionizationgauge is determined by a difference in the bias voltages between ananode grid and a collector post electrode. A bias voltage of a cathodeis typically at 30 volts, and a bias voltage of the anode grid istraditionally operated at 180 volts. The collector voltage is usuallyfixed at a ground potential, or at a voltage near a ground potential.These voltage differentials are configured to provide 150 electron volts(eV) amount of energy for the electrons. This amount is capable ofefficiently ionizing all gas species present in the gauge ionizationvolume. This potential difference also assures efficient transport ofthe electrons from the cathode to the anode volume. Efficient ionizationis needed to assure an adequate signal to noise ratio from the collectorat low gas density levels.

Operation of the anode grid at +180 volts results in energetic ionsarriving at the grounded collector posts during operation. Those ionsimpact on the collector surfaces with kinetic energies ranging frombetween 0 to 180 eV. This large energy end of this spread is consistentwith large sputtering yields.

For example, sputtering yields as large as 0.2 atoms/ion impact havebeen demonstrated for Ar⁺ ions impinging on a tungsten target with 200eV of kinetic energy. Ions also created outside of the anode grid canalso reach the envelope walls with kinetic energies as large as 180 eV.Such large kinetic energy also increases sputtering yields, and theseimpacts remove materials from the envelope walls and adjacentstructures.

The present disclosure decreases the anode grid voltage at high pressurelevels in order to decrease the yield of sputtering impacts. The presentionization gauge provides for a reduction in an anode grid voltage downto about 80 volts to provide for about a five fold decrease in thesputtering yields for Ar⁺ ions impinging on a tungsten collectorsurface. Reducing the cathode potential allows the anode to cathodevoltage difference to still provide electrons capable of causingadequate ionization of atoms and molecules.

The effects of both ion energy and electron emission current oncollector sputtering rates were experimentally tested in our laboratorythrough a long term study which tracked the operation of a large groupof Micro-Ion® gauges in 35 mTorr of argon gas for several months. Alltested gauges contained dual tungsten collectors of small initialdiameter. As expected, the rate of collector diameter erosion (i.e. dueto sputtering impacts between energetic argon ions and tungsten walls)was proportional to the electron emission current and highly dependenton ion energy. A change in grid voltage from 180V to 80V, representingan ion energy reduction from 180 to 80 eV, resulted in approximately15-fold reduction in sputtering yields exceeding the predictions of thetheoretical calculations based on current sputtering models. Gaugesoperated at reduced emission currents and reduced ion energies exhibitedalmost imperceptible collector erosion, no detectable signs ofmetallization of adjacent electrode structures and minimal change infilament operation parameters over time. The advantages of operation atlow electron emission currents and low ion energies were fullydemonstrated by this carefully monitored test.

There is provided an ionization gauge to measure pressure while reducingsputtering when operating at high pressure. The ionization gaugeincludes at least one electron source that generates electrons, and acollector electrode that collects ions formed by the collision betweenthe electrons and gas molecules. The ionization gauge also includes ananode. The anode is configured to switch a bias voltage relative to abias voltage of the collector electrode at a predetermined pressure todecrease a yield of sputtering impacts.

In one embodiment, the ionization gauge is configured so the anodeoperates at an initial bias voltage at one pressure range, such as, forexample, below about 10⁻⁴ Torr. Then at high pressure, the anodeoperates at a reduced bias voltage, such as, for example, pressuresabove about 10⁻⁴ Torr.

The ionization gauge may also have a controller. The controller changesthe bias voltage of the anode based on a pressure range of the pressurein the ionization gauge. The anode can switch the bias voltage so apotential difference between the anode and the collector is less than 90volts. In another embodiment, the bias voltage of the anode may beswitched so a potential difference between the anode and the collectoris about 80 volts. In yet another embodiment, the gauge may have anelectron source that operates at less than 20 volts, or that operates atabout 10 volts.

In a further embodiment of the present disclosure, the ionization gaugehas an anode grid, and the anode bias voltage can be switched from about180 volts to 80 volts. Alternatively, the bias voltage is switched fromabout 180 volts to another anode bias voltage. The anode may operate ata reduced bias voltage at pressure of above about 10⁻⁴ Torr.

The ionization gauge may further include that the collector electrodesurrounds the anode as a triode ionization gauge. Alternatively, thecollector electrode can be positioned outside of the anode. Theionization gauge may further include a second collector electrode. Thesecond collector electrode can be positioned outside the anode tocollect ions formed at high pressure. The ionization gauge can be of theBayard-Alpert type. The gauge may also include a cold cathode electronsource.

In yet another aspect of the present invention, there is provided amethod of measuring a gas pressure from gas molecules and atoms. Themethod includes producing electrons from at least one electron sourceand transmitting the electrons to an anode to form ions. Ions formed bythe collisions between the electrons and the gas molecules and atoms arecollected on the collector electrode. A bias voltage of an anoderelative to a bias voltage of the collector electrode is switched toreduce an impact energy of the ions on the ion collector.

The ion collector potential preferably is selected to be at a low nearground potential to avoid leakage currents to ground, especially for lowpressures when the ion collector current is relatively small. Thecathode filament potential is typically selected to about 30 voltspotential relative to ground, and also relative to the ion collectorpotential to avoid electrons arriving at the ion collector electrodewith a predetermined energy, and this is relevant for a combination ofhigh emission currents and low ion collector currents. The anodepotential is typically selected to be at about 180 volts relative toground.

A potential difference between the anode and the cathode determines theenergy of the electrons as they arrive at the anode. The potentialdifference is typically selected to be about 150 volts. The anode isrelatively higher than the cathode so that the energy of the electronsavailable for ionization of the gas is at about 150 electron volts. 150eV is at a fairly low slope of an ionization probability versus electronenergy curve for most gases. Therefore, at 150 eV an ionization gaugesensitivity variation with electron energy is minimized. It should beappreciated that this may depend on the specific gas species. Electronsare accelerated from the cathode to the anode at an energy of about 150eV. It should be appreciated that generally lower values of thispotential difference begins to allow the onset of space charge limitingof the electron emission from the cathode. Space charge limiting imposesan electron emission limit from the cathode and can bring on hightemperature operation and failure of the cathode since a typical controlcircuit attempts to supply power to the cathode until a desiredspecified electron emission current is achieved. Lowering the cathodepotential allows a lower anode potential to still achieve an acceptableanode to cathode potential difference without space charge limiting.

Secondly, a potential difference between the anode to the ion collectordetermines the maximum energy of the ions as they arrive at the ioncollector. Ions formed near the anode will have the maximum energy, andions formed relatively closer to the ion collector will have relativelyless energy. The potential difference between the anode to the cathodeor the gauge envelope is typically about 180 volts, and this dictatesthe energy and, thus, the impact of the ionized atoms and molecules whenthey arrive at the surface of the ion collector. The potentialdistribution in the anode has a shape such that a majority of the anodevolume is near the potential of the anode, and a majority of the ionsarriving at the ion collector have the maximum energy. The potentialdifference of the anode to cathode or gauge envelope also dictates theenergy of the ions formed outside of the anode volume when they finallyarrive at any relatively lower potential surfaces, such as, for example,the cathode, the collector shield, or an envelope of the gauge.

Altering the above mentioned potentials allows more electrons to arriveat the ion collector and reduces the measured ion collector current.However, more electrons will not change the positive ion currentarriving at the ion collector. It should be appreciated that themeasured collector current equals ions arriving at the collector minuselectrons arriving at the collector. Any change in the potentials thatwill reduce the number of ions created, such as ionization probability,or reduce the number of created ions that are collected will reduce theactual ion current to the ion collector.

The number of created ions collected is dependent on the ion energy andthe ion collector diameter, or ion collector geometry. At relatively lowpotential surfaces, sputtering is directly related to the number of ionscreated, the number of ions arriving at the surface of interest, and theenergy of those ions. The sputtering rate is relevant to the number ofatoms sputtered per unit time and relative to the number of incidentions per unit time. The sputtering yield is relevant to the number ofatoms sputtered per incident ion and is related to the energy ofincident ions. High pressure causes large ion currents, and consequentlyhigh pressure also causes large sputtering rates. By lowering the ionenergy diminishes the sputtering yield, which may decrease thesputtering rate even at a relatively high pressure.

According to yet another aspect of the present disclosure, there isprovided a process that includes providing a substrate, evacuating atool to perform processes on the substrate in the tool, and measuringpressure. The method for measuring pressure includes an electron sourcethat generates electrons, and an ionization volume in which theelectrons impact a gaseous substance that includes gas molecules andatoms. The anode grid voltage is decreased at high pressure levels inorder to decrease the yield of sputtering impacts. A collector electrodecollects ions formed by the impact between the electrons and the gaseoussubstance.

The gauge can be used in a process. The process includes conductingoperations on the substrate in the vacuum environment to form aprocessed substrate. In another embodiment, the process can includeoperations that are selected from the group consisting of operationsassociated with manufacture of a flat panel display, magnetic mediaoperations, solar cell manufacturing operations, optical coatingoperations, semiconductor manufacturing operations, and any combinationthereof. Operations may also include one or more processes selected fromthe group consisting of: physical vapor deposition, plasma vapordeposition, chemical vapor deposition, atomic layer deposition, plasmaetch operations, implantation operations, oxidation, diffusion, a vacuumlithography process, a dry strip operation, an epitaxy process, athermal processing operation, an ultraviolet lithography operation, andany combination thereof.

Preferably, current is converted from the collector electrode to apressure signal to measure pressure. The process may also includemeasuring a parameter of a process using an analytical tool. In oneembodiment, the analytical tool may measure a parameter of the wafer.The analytical tool can be selected from the group consisting of: ascanning electron microscope, an energy dispersive X-ray spectroscopyinstrument, a scanning auger microanalysis instrument, a glow dischargemass spectroscopy instrument, an electron spectroscopy chemical analysisinstrument, an atomic force microscopy instrument, a scanning probemicroscopy instrument, a Fourier transform infrared spectroscopyinstrument, a wavelength dispersive X-ray spectroscopy instrument, aninductively coupled plasma mass spectroscopy instrument, an x-rayfluorescence instrument, a neutron activation analysis instrument, ametrology instrument, and any combination thereof. A parameter of theprocess can be also measured using a mass spectrometer. The massspectrometer can be one of a gas chromatograph instrument, a liquidchromatograph instrument, an ion trap instrument, a magnetic sectorspectrometer instrument, a double-focusing instrument, a time-of-flightinstrument, a rotating field instrument, an ion mobility instrument, alinear quadrupole instrument, or any combination thereof. The ionizationgauge in the process preferably converts the current from the collectorelectrode to a pressure signal.

In yet another embodiment, a process may include a manufacturing processstep and then measuring a parameter of the process using an analyticaltool and measuring pressure. The pressure measurement is performed whiledecreasing the yield of sputtering impacts at high pressure. Theanalytical tool can be any mass spectrometer, or any previouslymentioned instrument.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a schematic view of a generalized ionization gauge of thepresent disclosure.

FIG. 2 is a detailed schematic view of a non-nude type ionization gaugeof FIG. 1.

FIG. 3 is a schematic view of an ionization gauge including an anodecoupled to an anode voltage supply for reducing an electron impactenergy at high pressures according to the present disclosure.

FIGS. 4 through 6 show several schematic views of embodiments ofionization gauges for collecting ions using a second collector at highpressure, and for extending the measuring range of the ionization gauge.

FIG. 7 shows a Schultz-Phelps ionization gauge of the presentdisclosure.

FIG. 8 shows the ionization gauge of FIG. 3 used with a cluster tool andan analytical tool for processing operations.

DETAILED DESCRIPTION OF THE INVENTION

A description of preferred embodiments of the invention follows.

Generally, as shown in FIG. 1, an ionization gauge 100 of the presentdisclosure has at least one electron source 105 and at least onecollector electrode 110. The electron source 105 may be separated fromthe at least one collector electrode 110 by an optional isolationmaterial 115 which prevents molecules and atoms of gas within ameasurement chamber 117 from degrading the electron source(s) 105. Theionization gauge 100 also includes an ionization volume and specificallyan anode 120. Anode 120 and the collector electrode 110 components mayhave various different configurations, and the gauge 100 is not limitedto FIG. 1. In one embodiment, the ionization gauge 100 is aBayard-Alpert type gauge, or an ionization gauge 100 where a heatedcathode 105 is used to emit electrons toward an anode grid volume 120.However, it should be appreciated that the gauge 100 is not limited toany specific ionization gauge configuration and the present inventionencompasses several different types of gauges.

The Bayard-Alpert type gauge 100 is based on the ionization of gasmolecules by a constant flow of electrons. The negatively chargedelectrons shown as reference numeral 125 are emitted at awell-controlled selectable rate from a heated cathode 105, and may bereleased, or accelerated toward a positively charged anode 120. Theelectrons 125 pass into and through the anode 120 and then cycle backand forth through the anode 120. The electrons 125 are then retainedwithin the ionization volume of the anode 120. In this space, theelectrons 125 collide with the gas molecules to produce positivelycharged ions. These ions are collected by the one or more ioncollector(s) 110. Collector 110 is nearly at ground potential, which isnegative with regard to the positively charged anode 120. However, thisarrangement is not limiting and collector 110 may have various potentialdifferences with respect to the anode 120. At a constant cathode toanode voltage and electron emission current, the rate that positive ionsare formed is directly correlated to the density of the gas in the gauge100. This signal from the collector electrode 110 is detected by anammeter 135, which is calibrated in units of pressure, for all pressurereadings.

The embodiment of FIG. 1 is shown as a nude configuration of theBayard-Alpert type gauge 100. It is also envisioned that non-nude typeionization gauges are also possible. FIG. 2 shows a specific non-nudetype ionization gauge 200 embodying the present disclosure. Theionization gauge 200 has similar components to the ionization gauge 100(FIG. 1) described above with the following additions. The ionizationgauge 200 is housed in a tube 205. Tube 205 is opened at one end 225 toallow molecules and atoms of gas to enter the measurement chamber 117through a shield 220. The shield 220 and tube 205 form a shield volume.An optional second ion collector 210 is added for high pressuremeasurements of very short mean free paths.

In operation, molecules and atoms of gas enter the measurement chamber117 through the partially open shield 220. The shield 220 preventspotentials external to the shield 220 from disturbing the electriccharge distribution within the measurement chamber 117. The shield 220is maintained at a reference potential. In one embodiment, the referencepotential is ground potential.

Turning now to FIG. 3 the electron source (for example, a cathodefilament) 105 generates electrons (represented by an electron beam 125)within the chamber 117 defined by the envelope 113. The electrons 125are used in ionizing the gas molecules in the measurement chamber 117.The geometrical shape of the filament 105 can be a linear ribbon, alinear wire, a straight ribbon, a curved ribbon, a hairpin wire, or anyother shape known in the art. In one embodiment, the cathode 105 isresistively heated to incandescence with an electrical current fromcathode heating power supply 113. The thermionically emitted electrons125 may be released, or accelerated or directed into the measurementchamber 117 towards anode 130. Electrons have a sufficient energy whichallows the electrons to be transmitted to the ionization volume of anode130 and have sufficient energy to enter the anode 130.

A controller 105 a is connected to the cathode bias supply 105 b, andthe cathode 105 receives a cathode bias voltage of about 30 volts, and aheating voltage from power supply 113 during normal operation. Once thecathode 105 is sufficiently heated, the controller 105 a controls thecathode 105 to maintain the appropriate electron current. The cathodebias voltage provides sufficient voltage difference from the cathode 105to the anode 130 to transmit electrons 125 toward the anode grid 130.Ionization occurs over an energy spread both higher and lower than thenominal design energy; see Section 5.7 on ionization gauges inScientific Foundations of Vacuum Technique by Saul Dushman, 1962, whichis herein incorporated by reference in its entirety.

The controller 105 a also is coupled to the anode voltage supply 130 a,which delivers a bias voltage to the anode wire grid 130. The anode 130includes an anode bias voltage of about 180 volts when measuringpressure at high vacuum conditions. This difference (180 volts minus 30volts) provides for 150 eV of energy for the electrons. This is theamount of kinetic energy that is gained by a single free electron 125,when the electron 125 passes through a potential difference that iscreated between the cathode 105 and the anode grid 130. This 150 eV issufficient to ionize all gas species present in the ionization gaugevolume at high vacuum conditions.

These ionized atoms and molecules can have a maximum energy of about 180eV when arriving at the ion collector 110. These ions formed in theionization volume of the anode 130 will impact on the collector surface110, and when operating at high pressure, this large quantity of ionsmay be excessive and can increase the sputtering rate for unit time. Asmentioned, sputtering yields can be as large as 0.2 atoms/ion for Ar⁺ions impacting on tungsten targets with 200 eV kinetic energies, andthis kinetic energy can damage the components of the gauge 100 anddegrade the ionization gauge 100. To counteract high sputtering rates,an ionization gauge design may also decrease sputtering yields.

The present ionization gauge 100 decreases anode grid bias voltagelevels relative to the bias voltage of the collector 110 at highpressure levels to decrease the yield of sputtering collisions. Areduction of the anode grid bias voltage to about 80 volts can providefor about a five fold decrease in the sputtering yield for Ar⁺ ionsimpacting on a tungsten surface of a collector electrode 110. Althoughreducing the bias voltage of the anode grid 130, the energy of theelectrons remains sufficiently high for their collisions with gas atomsand molecules to ionize all gas species present in the ionization volumein the anode grid 130. At the same time, the kinetic energy of the ionsis decreased to lessen the energy of ions arriving at the collector 110,envelope walls, and adjacent grounded electrode structures (not shown).This occurs while providing sufficient potential difference betweencathode 105 and anode 130 so electrons 125 can enter the anode gridvolume 130 while reducing sputtering yields.

Notably, a byproduct of the bias voltage reduction can be a decrease ina sensitivity of the ionization gauge 100. Since this reduction occursat high pressure levels, or above 10⁻⁴ Torr, the ion current signalreceived by the collector electrode 110 is relatively large. Thisreceived signal/noise level by the collector 110 is adequate foroperation of the ionization gauge 100.

In a first embodiment, the ionization gauge 100 includes that thecontroller 105 a, reduces a bias voltage of the anode grid 130 in a highpressure mode. In the embodiment shown, preferably the controller 105 asufficiently reduces the bias voltage supplied to the anode grid 130 bycontrolling anode voltage supply 130 a. The anode grid 130 operates atan anode bias voltage of less than 180 volts. This reduced bias voltageresults in reduced electron kinetic energy from 150 eV, or the potentialdifference between the cathode 105 and the anode grid 130.

Notably, this reduced electron kinetic energy of less than 150 eV isstill sufficient to ionize all gas species present in the ionizationgauge 100 volume. The values of threshold ionization energies requiredfor different monatomic species can range from 3.88 eV (Cs) to 24.58 eV(He), and 15 eV (for oxygen, nitrogen, and hydrogen). Various ionizationenergies are possible and are within the scope of the presentdisclosure, depending on the gaseous material that is desired to bemeasured.

In another embodiment, the controller 105 a outputs a control signal tothe anode voltage supply 130 a to reduce the anode bias voltage supplyfrom 180 volts to 80 volts, or less. In this embodiment, the electronenergy, or difference between the bias voltage of the cathode 105 andthe anode 130 is 50 eV. This amount is sufficient to ionize the gas athigh pressures without causing the degradation of the ionization gauge100 that is attributed to high sputtering yields. This results in adecrease in the yield of sputtering impacts for Ar⁺ ions impinging ontungsten collector electrode 110 surface, and this 50 eV value mayprovide for a five-fold decrease in the sputtering yield. It should beappreciated that other anode bias voltages are also envisioned, and thepresent ionization gauge 100 is not limited to any specific anode biasvoltage reduction.

In one embodiment, the ionization gauge 100 is configured so the anode130 operates at an initial bias voltage at one pressure and thenautomatically operates at a reduced bias voltage at high pressures, suchas, for example, above about 10⁻⁴ Torr. The controller 105 a can switchautomatically the bias voltage so a potential difference between theanode 130 and the collector electrode 110 is less than 90 volts.

In another embodiment, the bias voltage of the anode 130 may be switchedfrom about 180 volts to about 80 volts so a potential difference betweenthe anode 130 and the collector electrode 110 is about 80 volts. Thecathode filament 105, can be supplied less than 20 volts, or can besupplied at about 10 volts so that an adequate voltage difference fromthe cathode 105 to the anode 130 is maintained. The anode 130 canoperate at a reduced bias voltage at high pressures or above about 10⁻⁴Torr.

At low pressure, where high sputtering yields are not as much of aconcern relative to the high pressure conditions discussed above, thecontroller 105 a may control the anode bias voltage supply 130 a toincrease the anode bias voltage supply. The potential difference can beincreased for sufficient ionization energies. This ensures that theelectrons have sufficient energy to efficiently ionize a very lowdensity of gas.

It should be appreciated that the bias voltage of the cathode 105 cannotbe too low, and has to be above the collector electrode 110, and theenvelope wall 113. Preferably, the cathode 105 is about 10 volts abovethe collector electrode 110.

The present ionization gauge 100 is not limited to controlling the biasvoltage of the anode grid 130. It is envisioned that the bias voltage ofthe filament 105 and the collector electrode 110 can also be modified bycontroller 105 a. The bias voltage of the filament 105 and the collectorelectrode 110 can also be modified by controller 105 a to minimizesputtering yields, and to extend the life of the ionization gauge 100.It should also be appreciated that the ionization gauge 100 may beconfigured as a triode ionization gauge (not shown) or another specifictype of gauge 100. It should be appreciated that the present ionizationgauge 100 is not limited to a BA ionization gauges, and may include acold cathode electron emitter 105.

The energy of the ions can be determined by the difference between theion collector 110 and the anode 130. Here, the anode 130 can be keptconstant and the collector 110 can be raised above ground potential toreduce the energy of the ions.

Turning now to FIG. 4, there is shown another embodiment of the presentdisclosure. Here, the ionization gauge is a Bayard-Alpert ionizationgauge 400; however, gauge 400 can alternatively be manufactured as acold electron emitter ionization gauge 400 with a cold electron emittersource. Gauge 400 includes an anode grid 430, a cathode filament 405,and a first ion collector electrode 410 a. The anode 430 surrounds thefirst ion collector electrode 410 a.

Typically, Bayard-Alpert ionization gauges are used to measure pressurein the high vacuum and ultrahigh vacuum environment. Pressuremeasurement capabilities become compromised at high vacuum levels or atabout 10⁻⁴ Torr, and become even more limited at about 10⁻³ Torr. Oneobserved problem is that at higher pressures electrons scatter on theirway to the anode grid 430. Long electron trajectories are compromised byscattering collisions with neutral species. Additionally, the ability toeffectively collect ions inside the anode 130 is compromised as the iondensity builds up around the collector post 410 a.

The present ionization gauge 400 preferably collects ions at highpressure that are located outside of the anode grid 430. This collectionextends the effective pressure operating range above 10⁻⁴ Torr.

In this embodiment, a second ion collector 410 b can be positioned in alocation near or closer to the cathode filament 405. Collector electrode410 b assures efficient collection of ions, which are located near theelectron source 405 at high pressures. Collector electrode 410 b isconfigured for use as an alternative second ion collector electrode 410b to collect ions formed outside of the anode 430 at high pressures.Second collector electrode 410 b extends the operating range of thegauge 400 to levels above 100 mTorr with a minimum detectable pressurelimit as low as 10⁻⁵ Torr. This provides for better overlap with a heatloss or a capacitance diaphragm pressure sensor in a combination gauge.This also provides for no lost time attributed to sensor switchingduring process cycles in PVD, semiconductor, and hard disk manufacturingprocesses. This also preserves the base measurement capabilitiesexpected from the gauge 400 and which are needed for a vacuumqualification of the instrument.

The ionization gauge 400 may also include that the second ion collectorelectrode 410 b is positioned near the filament 405, and is supported inan extra filament support post (not shown). This is advantageous in aretrofit installation of the second ion collector electrode 410 b to anexisting gauge. In yet another alternative embodiment, the secondcollector electrode 410 b is supported in another support structure,such as, for example, a support post which is located near the anodegrid 430. Various support configurations are possible.

The second ion collector electrode 410 b can be a post 410 b as shown inFIG. 4, or an electrode plate 410 c (FIG. 5), or can be formed as anelectrode grid or wall 410 d (FIG. 6). The second ion collectorelectrode 410 c of FIG. 5 can be connected to an ammeter 435 a, or mayalternatively be operatively coupled to the collector electrode 410 a,which is connected to the ammeter 435. The second collector 410 b can beconnected to a different ammeter 435 a, or the same ammeter 435 ascollector 410 a to measure ions, and gauge 400 is not limited to anyspecific configuration.

Turning to FIG. 6, the second ion collector may be formed as anintermediate wall 410 d. Collector wall 410 d surrounds the anode 430and the first ion collector electrode 410 a and the cathode 405.

The intermediate wall 410 d may be connected to a switch 440 (FIG. 6).Switch 440 provides for two modes of collecting ions, namely a highpressure operation mode and a normal (high vacuum) operation mode. Inthe high pressure operation mode, the ionization gauge 400 collects ionsusing the second ion collector grid or wall 410 d. In normal (highvacuum) operation mode, the first ion collector electrode 410 a collectsions. Gauge 400 can be switched between collecting ions using collector410 a or collector 410 d using switch 440, which can be manuallycontrolled or electronically controlled. Pressure is measured usingdetected signals received by the ammeter 435 which is connected to thecontroller 450. One collector would be used at high pressures, while ata different pressure, the other collector electrode would be used tomeasure pressure.

The intermediate wall 410 d can advantageously be installed in aretrofit manner to existing BA ionization gauges 400. In this aspect, aswitch 440 can be installed in a retrofit manner and connected betweenthe ammeter 435 and the first ion collector electrode 410 a in anexisting BA ionization gauge 400.

It should be appreciated that the cathode emission level may remainconstant, as well as, the voltage bias on the anode 430. In oneembodiment, the ammeter 435 would detect a pressure of 1×10⁻⁴ Torr, andthen output a signal to a controller 450. The controller 450, inresponse, would then switch from collecting ions using the first ioncollector electrode 410 a to collecting ions using the second ioncollector 410 d to collect ions formed closer to the filament 405.

In another embodiment, the ion current measurement may effectivelyself-switch from one collector to another collector whereby the ioncurrent diminishes significantly from the inside collector as thepressure increases from above about 10⁻³ Torr, and then diminishessignificantly from the outside collector as the pressure decreases below10⁻³ Torr. It should be appreciated that ion current from the outsidecollector is generally not a concern below 10⁻⁴ Torr.

It should be appreciated that the ionization gauge 400 may be formedwith more than two ion collector electrodes 410 a, 410 d. Gauge 400 mayinclude a second ion collector 410 d, and a third ion collectorelectrode (not shown), or more collector electrodes being placed nearthe filament 405 to collect ions at high pressures. Variousconfigurations are possible and within the scope of the presentdisclosure.

In another embodiment shown in FIG. 7, an ionization gauge 100 may beconfigured in a Schultz-Phelps geometry with the anode 115 beingarranged as a flat plate, the ion collector 110 as a parallel flatplate, and the electron source 105 positioned between those two plates110, 115.

Turning to FIG. 8, the ionization gauge 100 preferably can be used witha cluster tool 800 or another multi-chamber tool for processingoperations. In one embodiment, the cluster tool 800 may include a loadlock chamber 805 connected to a transfer chamber 810 by a valve 810 a.The load lock chamber 805 is sealed from ambient conditions by a valve810 b. Both a single chamber and multi-chamber cluster tools 800 areenvisioned, and the ionization gauge 100 can be used in either a singlechamber or a multi-chamber tool configuration. It should be appreciatedthat the ionization gauge 100 is not limited for use with a vacuumchamber, and can be used in any manufacturing chamber known in the art.

The cluster tool 800 may also include a process module 815. Processmodule 815 is also connected to the transfer chamber 810 by a valve 810c. The tool 800 may includes multiple process modules 815 and multipleload lock chambers 805, and the configuration shown is not limiting. Theload lock chamber 805 may include a rough pump RP1, which also isconnected to the load lock chamber 805 by a valve V₁. Each of the loadlock chamber 805, the transfer chamber 810, and the process module 815may include at least one vacuum pump Vp₁, Vp₂, and Vp₃. The vacuum pumpmay be a cryogenic vacuum pump, or another pump, such as a turbo pump orwater vapor pump. Various pumping configurations are possible and withinthe scope of the present disclosure.

Preferably, a wafer (not shown) may be introduced into the load lockchamber 805, and pumped to vacuum conditions using the rough pump Rp₁and the vacuum pump Vp₁. Using a wafer manipulating robot (not shown),the wafer can be manipulated to the transfer chamber 810 through thevalve 810 a, and then the wafer can be placed in the process module 815through the valve 810 c for various deposition operations. In oneembodiment, the ionization gauge 100 may be placed in one of thechambers 805, 810, or 815 of the cluster tool 800. For illustrationpurposes, the ionization gauge 100 is shown in the process module 815,but is not limited to any specific chamber or location, and can beplaced outside of the chamber or tool 800.

The ionization gauge 100 preferably can measure pressure both basepressure (high vacuum) and higher processing pressures (mostly in themTorr range), however this is not limiting and various operationalparameters for measurement are possible and within the scope of thepresent disclosure. The ionization gauge 100 can be used to measurepressure in the manufacture of flat panel displays, magnetic mediaoperations, solar cells, optical coating operations, semiconductormanufacturing operations, and other manufacturing process operations.Such processes may include physical vapor deposition, plasma vapordeposition (PVD), chemical vapor deposition (CVD), atomic layerdeposition (ALD), plasma etch operations, implantation operations,oxidation/diffusion, forming of nitrides, vacuum lithography, dry stripoperations, epitaxy operations (EPI), rapid thermal processing (RTP)operations, extreme ultraviolet lithography operations, and others.Preferably, the ionization gauge 100 may also be operable with one ormore analytical tools, such as, for example, a microscope or a massspectrometer. Mass spectrometers may include gas chromatographinstruments (GC), liquid chromatograph instruments (LC), ion trapinstruments, magnetic sector spectrometers instruments, double-focusinginstruments, time-of-flight instruments (TOF), rotating fieldinstruments, ion mobility instruments, linear quadrupole instruments,and others.

Surface analytical instruments 820 that can be used in connection withthe ionization gauge 100, and with the cluster tool 800 (or without thecluster tool 800) may also include scanning electron microscopes, energydispersive X-ray spectroscopy instruments (EOS/XPS), scanning augermicroanalysis instruments (Auger/SAM), glow discharge mass spectroscopyinstruments (GDMS), electron spectroscopy for chemical analysisinstruments (ESCA), atomic force microscopy/scanning probe microscopyinstruments (AFM/SPM), Fourier transform infrared spectroscopyinstruments (FTIR), wavelength dispersive X-ray spectroscopy instruments(WDS), inductively coupled plasma mass spectroscopy instruments (ICPMS),x-ray fluorescence instruments (XRF), neutron activation analysisinstruments (NAA), metrology instruments, and others. It should beappreciated that this listing is not exhaustive and the gauge 100 may beused with other instruments not enumerated above.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. An ionization gauge to measure pressurecomprising: an anode enclosing a volume; an electron source thatgenerates electrons outside of the anode; an inside ion collectorelectrode, located inside of the anode, that collects ions formed by theimpact between the electrons and gas molecules and atoms inside theanode; and an outside ion collector electrode, located outside of theanode, that collects ions formed by the impact between the electrons andgas molecules and atoms outside the anode, the outside ion collectorelectrode being closer than the inside ion collector electrode to theelectron source, to collect ions at pressures above about 10⁻⁴ Torr. 2.The ionization gauge of claim 1, wherein the bias voltage of the anodeis switched to a reduced level during normal operation with pressureabove 10⁻⁴ Torr to decrease a yield of sputtering collisions.
 3. Anionization gauge as claimed in claim 1, further comprising a switch thatprovides for collection of the ions using the outside ion collectorelectrode in a high-pressure mode of operation and collection of ionsusing the inside ion collector electrode during a normal mode ofoperation.
 4. The ionization gauge of claim 1, wherein the outside ioncollector surrounds the anode, the inside ion collector electrode andthe electron source.
 5. A method of measuring a gas pressure from gasmolecules and atoms, comprising the steps of: producing electrons froman electron source outside of an anode; transmitting the electrons tothe anode to form ions; collecting ions formed by impact between theelectrons and gas molecules and atoms inside the anode with an insideion collector electrode located inside the anode; and collecting ionsformed by impact between the electrons and gas molecules and atomsoutside of the anode with an outside ion collector electrode, locatedoutside the anode and closer than the inside ion collector electrode tothe electron source, at pressures above about 10⁻⁴ Torr.
 6. The methodof claim 5, wherein the bias voltage of the anode is switched to areduced level during normal operation with pressure above 10⁻⁴ Torr todecrease a yield of sputtering collisions.
 7. The method of claim 5,further comprising switching between collection of the ions using theoutside ion collector electrode in a high-pressure mode of operation andcollection of ions using the inside ion collector electrode during anormal mode of operation.
 8. The method of claim 5, wherein the outsideions collector surrounds the anode, the inside ion collector electrodeand the electron source.
 9. An ionization gauge to measure a pressurecomprising: an anode enclosing a volume; an electron source thatgenerates electrons; a low-pressure ion collector electrode, located toa side of the anode opposite to the electron source, that collects ionsformed by the impact between the electrons and gas molecules and atomsat low pressures; and a high-pressure ion collector electrode, locatedto a same side of the anode as the electron source, that collects ionsformed by the impact between the electrons and gas molecules and atoms,the high-pressure ion collector electrode being closer than thelow-pressure ion collector electrode to the electron source to collections at ion pressures above about 10⁻⁴ Torr.
 10. A method of measuringgas pressure from gas molecules and atoms comprising the steps of:releasing electrons from an electron source; transmitting the electronsthrough an anode enclosing a volume to form ions; collecting ions formedby the impact between the electrons and gas molecules and atoms with alow-pressure ion collector electrode to a side of the anode opposite tothe electron source; and at pressures above about 10⁻⁴ Torr, collectingions formed by impact between the electrons and gas molecules and atomsto a same side of the anode as the electron source with a high-pressureion collector electrode that is closer than the low-pressure ioncollector electrode to the electron source.